Serendipity of a topological nontrivial band gap in the 2D borophene subunit lattice with broken mirror symmetry.

Abstract

The exotic electronic band structures featured by Dirac cones and topological phases in two-dimensional (2D) materials are regarded as the holy grail of the next-generation electronic devices. Here we propose a 2D tungsten boride (WB4) lattice to concurrently host these interesting properties. Based on first-principles calculations, we demonstrate that in the absence of spin-orbit coupling (SOC), the mirror symmetry protects the WB4 lattice to spawn multiple Dirac bands around the Fermi level with high velocities. However, the broken mirror symmetry induces one cone to be opened with a small band gap, and gives rise to a nontrivially topological phase characterized by the non-zero Z2 topological invariant. Interestingly, topologically nontrivial states of the lattice without mirror symmetry are robust within external biaxial tension, which is confirmed from the appearance of gapless edge states in their nanoribbon structure. Our results provide a versatile platform for hosting nontrivial topological states usable for important nanoelectronic device applications.